This invention relates to sonar systems and more particularly to adjustable delay lines for sonar systems.
Infrasonic, sonic, and ultrasonic sound delay lines are used in a wide variety of applications, ranging from delaying one signal with respect to another e.g. in phased transducers for radar and sonar systems to storage elements for computer systems. For many of these applications it would be desirable to vary the length of the delay time. Since the velocity of infrasonic, sonic, and ultrasonic sound waves in a solid are directly proportional to the square root of the elasticity, changing the elasticity of the material is one way the delay time may be changed.
The possibility of a change in elasticity with magnetization was reported more than one hundred years ago. (See R. M. Bozorth, Ferromagnetism, 684 (D. Van Nostrand Co., New York, 1951)). The biggest effects were found in soft magnetic materials with large magnetostrictions such as well-annealed Ni. Typical values for .DELTA.E/E.sub.o are .01 to 0.10, which, in fact, scatter from sample to sample. For Ni, at room temperature, values range from 0.06 to 0.18. For annealed Fe, .DELTA.E/E.sub.o .perspectiveto. .004. The maximum change in velocity for infrasonic, sonic, and ultrasonic waves in nickel which can be achieved by generating a magnetic field in the nickel is only from about 3 to about 9 percent. Thus, while the use of magnetic fields is a convenient way to vary the velocity of sound waves in solids, the changes in velocity available in the prior art are so small as to have very limited if any practical applications. Therefore, it would be desirable to find devices or methods which would be capable of substantially altering the velocity of infrasonic, sonic, and ultrasonic sound waves by applying magnetic fields.